Many players like to camp with the RPG and wait for another player to wander into their line of sight. This works well when not in close combat. A popular place to do this is in the top of the Alpha side of the cross-spawn vent in Overdose. A player will wait, shoot, then retreat to pull out another gun to finish off the severely injured enemy player.
Another despised tactic is to switch between the RPG and LAW while they reload, making it possible to fire 2 shots quickly, thus making it extremely easy to get massive amounts of kills in one life.
Another way it is used, typically by more skilled players, involves having an RPG and an assault rifle, shooting the RPG (hopefully avoiding self-inflicted damage), then quickly drawing the assault rifle to finish off the enemy player. This works well in Junk Flea and other small, open maps. Also another favorite camping spot with the RPG is behind the map in Grave Digger (as shown below) where they can avoid taking damage from themselves and severely injure the player coming through the door. This also works well if there is another player with the RPG camper able to finish off or injure the player before the RPG camper fire the RPG.
Another method for long range shooting is to scope in using a sniper or any scoped gun, then switch to the RPG. This will help getting more precise shots nearer to your enemies, thus causing more damage and deaths. This is really effective in Kill Creek, where it is suggested you scope, duck, switch to RPG, stand, and fire immediately.The only drawback is that any smart enemy will run or, if skilled, will shoot the RPG while it is flying.
Aim for the floor near the enemies in open spaces because if you miss, the rocket would keep going, and the explosion would NOT kill the target, leaving you defenseless.